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Homework Help: Electric Potential and Field

  1. Oct 17, 2008 #1
    1. The problem statement, all variables and given/known data

    The potential as a function of position in a region is given by V(x) = 3x - 2x^2 - x^3. (x in meters and V in volts). Find equation for electric potential field.

    2. Relevant equations

    v = integral(E * dr)

    3. The attempt at a solution

    I tried taking the derivative of v to get E but it keeps says im missing something. So first i tried, 3-4x-3x^2 but its off by a multiple and than i figured since v is the integral of E * displacement --> meaning the derivative of V is E so i got what i got before and decided to divide by X which got me 3/x - 4 - 3x which also didnt work.

    Im not sure quite what to do.
  2. jcsd
  3. Oct 17, 2008 #2
    The electric field is given by

    [tex] E = - \vec{\nabla}V [/tex]

    In this case,

    [tex] E = -\frac{dV}{dx} [/tex]

    Your forgetting the minus sign.
  4. Oct 17, 2008 #3
    ah ok ;) makes sense.

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